Re: [PATCH v2 5/5] watchdog: qcom: add support to read the restart reason from IMEM

[Bryan O'Donoghue <bod.linux@nxsw.ie>]

On 16/04/2025 09:29, Kathiravan Thirumoorthy wrote:
> When the system boots up after a watchdog reset, the EXPIRED_STATUS bit
> in the WDT_STS register is cleared. To identify if the system was restarted
> due to WDT expiry, bootloaders update the information in the IMEM region.
> Update the driver to read the restart reason from IMEM and populate the
> bootstatus accordingly.

Which bootloaders ?

Do you mean bootrom or one of the subsequent phase bootloaders ?

Please be specific about which bootloader populates this data i.e. if I 
switch my bootloader to u-boot do I loose the added flag ?

> For backward compatibility, keep the EXPIRED_STATUS bit check. Add a new
> function qcom_wdt_get_restart_reason() to read the restart reason from
> IMEM.
> 
> Signed-off-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@oss.qualcomm.com>
What I'd really love to see here is an example of reading out the data 
from sysfs.

How do I as a user/consumer of this new functionality parse the new data 
it provides ?

Ideally do this in the commit log and recommend doing it in the cover 
letter to, as people don't always read both when commenting on patches.

> ---
> Changes in v2:
> 	- Use the syscon API to access the IMEM region
> 	- Handle the error cases returned by qcom_wdt_get_restart_reason
> 	- Define device specific data to retrieve the IMEM compatible,
> 	  offset and the value for non secure WDT, which allows to
> 	  extend the support for other SoCs
> ---
>   drivers/watchdog/qcom-wdt.c | 47 +++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index 006f9c61aa64fd2b4ee9db493aeb54c8fafac818..94ba9ec9907a19854cd45a94f8da17d6e6eb33bc 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -7,9 +7,11 @@
>   #include <linux/interrupt.h>
>   #include <linux/io.h>
>   #include <linux/kernel.h>
> +#include <linux/mfd/syscon.h>
>   #include <linux/module.h>
>   #include <linux/of.h>
>   #include <linux/platform_device.h>
> +#include <linux/regmap.h>
>   #include <linux/watchdog.h>
> 
>   enum wdt_reg {
> @@ -39,6 +41,9 @@ static const u32 reg_offset_data_kpss[] = {
>   };
> 
>   struct qcom_wdt_match_data {
> +	const char *compatible;
> +	unsigned int restart_reason_offset;
> +	unsigned int non_secure_wdt_val;
>   	const u32 *offset;
>   	bool pretimeout;
>   	u32 max_tick_count;
> @@ -175,6 +180,15 @@ static const struct watchdog_info qcom_wdt_pt_info = {
>   	.identity	= KBUILD_MODNAME,
>   };
> 
> +static const struct qcom_wdt_match_data match_data_ipq5424 = {
> +	.compatible = "qcom,ipq5424-imem",
> +	.restart_reason_offset = 0x7b0,
> +	.non_secure_wdt_val = 0x5,
> +	.offset = reg_offset_data_kpss,
> +	.pretimeout = true,
> +	.max_tick_count = 0xFFFFFU,
> +};
> +
You should separate the addition of your compatibles and their 
descriptor tables from generic functional extensions.

i.e. add the compat string and the above table in a subsequent patch.

>   static const struct qcom_wdt_match_data match_data_apcs_tmr = {
>   	.offset = reg_offset_data_apcs_tmr,
>   	.pretimeout = false,
> @@ -187,6 +201,29 @@ static const struct qcom_wdt_match_data match_data_kpss = {
>   	.max_tick_count = 0xFFFFFU,
>   };
> 
> +static int  qcom_wdt_get_restart_reason(struct qcom_wdt *wdt,
> +					const struct qcom_wdt_match_data *data)
> +{
> +	struct regmap *imem;
> +	unsigned int val;
> +	int ret;
> +
> +	imem = syscon_regmap_lookup_by_compatible(data->compatible);
> +	if (IS_ERR(imem))
> +		return PTR_ERR(imem);
> +
> +	ret = regmap_read(imem, data->restart_reason_offset, &val);
> +	if (ret) {
> +		dev_err(wdt->wdd.parent, "failed to read the restart reason info\n");
> +		return ret;
> +	}
> +
> +	if (val == data->non_secure_wdt_val)
> +		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +
> +	return 0;
> +}
> +
>   static int qcom_wdt_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> @@ -267,8 +304,13 @@ static int qcom_wdt_probe(struct platform_device *pdev)
>   	wdt->wdd.parent = dev;
>   	wdt->layout = data->offset;
> 
> -	if (readl(wdt_addr(wdt, WDT_STS)) & 1)
> -		wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +	ret = qcom_wdt_get_restart_reason(wdt, data);
> +	if (ret == -ENODEV) {
> +		if (readl(wdt_addr(wdt, WDT_STS)) & 1)
> +			wdt->wdd.bootstatus = WDIOF_CARDRESET;
> +	} else if (ret) {
> +		return ret;
> +	}
> 
>   	/*
>   	 * If 'timeout-sec' unspecified in devicetree, assume a 30 second
> @@ -322,6 +364,7 @@ static const struct dev_pm_ops qcom_wdt_pm_ops = {
>   };
> 
>   static const struct of_device_id qcom_wdt_of_table[] = {
> +	{ .compatible = "qcom,apss-wdt-ipq5424", .data = &match_data_ipq5424 },
>   	{ .compatible = "qcom,kpss-timer", .data = &match_data_apcs_tmr },
>   	{ .compatible = "qcom,scss-timer", .data = &match_data_apcs_tmr },
>   	{ .compatible = "qcom,kpss-wdt", .data = &match_data_kpss },
> 
> --
> 2.34.1
> 
>